Powder processing of metals includes capacitive discharge sintering, direct metal laser melting, electron beam melting, and other techniques. These processes have been used to create near net shape parts, and occasionally to control microstructure. This microstructure control is limited to grain size and grain orientation control. This control is all dependent on heat input. What is desired is to control nucleation and growth kinetics within the structure independent of, or in conjunction with, thermal input.
Prior art exists in which nanoparticles are used in melts to help seed crystallization. This is usually accomplished by adding nanoparticles into a molten alloy, physically distributing them, and then casting the resulting material. These nanoparticles are generally ceramic because they must be added and mixed in the melt. Metal particles and certain desirable ceramic particles would likely be dissolved and therefore cannot be used in this prior-art process. The microstructures which develop during such processing can be easily attributed to the casting process. The microstructures have nanoparticles segregated to the interdendritic regions. See, for example, Chen et al., “Rapid Control of Phase Growth by Nanoparticles,” Nature Communications, 5:3879, May 2014; and Xu et al., “Theoretical Study and Pathways for Nanoparticle Capture during Solidification of Metal Melt,” Journal of Physics: Condensed Matter, 24 (2012) 255304.
There are no known methods to develop three-dimensional nanoparticle architectures within metal microstructures. These architectures could significantly improve material properties by impeding, blocking, or redirecting dislocation motion in specific directions. This could be used to control failure mechanisms well beyond anything available in isotropic or anisotropic materials today.
Generally, improved methods of controlling solidification in powder materials, and compositions suitable for such methods, are needed. Preferably, the control of solidification does not require active, dynamic adjustment of reaction parameters during the solidification process.